i found that sitting bub on your lap and holding there arms above their head for a few secs then repeat it till a burp worked well!!
up over the shoulder and a bit of a pat on the back worked too but sounds like youve already tried that !!

nixon always burps when someone picks him up... spesh when grandma comes round... when ppl are in his face saying oohh how cute little baby etc... they get a burp in there face ... its funny....
burp